This invention relates generally to generating electrical power and, more particularly, to using a fluid under pressure to generate electrical power where the fluid under pressure is also being used for other purposes and the amount of pressurized fluid available to generate electrical power varies. For example compressed air used in a rail car braking system.
Electrical power is utilized on board a railcar by electronic devices and controls for such functions as electronically controlled pneumatic brakes, sensing for diagnostics, communications (e.g. asset tracking) and GPS functions. Traditional railcars have no electrical power available. It is known to generate voltage, e.g. 230 volts DC (at several kW) in a locomotive and to run the voltage over an entire train length. Since two connectors per car are required to extend the voltage over the entire train, multiple possibilities exist for single point failure, thus making reliability a serious concern. In addition, the entire train must employ all-electronic railcars, i.e. electronic railcars cannot be mixed with traditional railcars that contain no electronics. This non-mixing limitation may lead to problems in new product deployment.
Another known method for providing electrical power is not subject to the above-described limitations. Power is generated on each car by an axle-mounted generator that supplies a load and also charges a battery. Energy from the battery is used to power railcar electronics when the car is at rest or is moving slowly. Battery lifetime, however, is presently limited to approximately five years. There are also reliability concerns associated with a harsh environment for the axle-mounted generator and wires required for distributing power from the generator to a point of use.
It would be desirable to provide a reliable method for generating power on a railcar that is long lived and essentially transparent to a railcar user, i.e. does not require unusual maintenance for the railcar or other train systems. It also would be desirable to provide an energy source for powering an electronically controlled air brake on a pressurized railcar that functions while the car is at rest, in the dark, and with no wind blowing. It also would be desirable to be able to use compressed air already available on a railcar for efficiently generating electrical power with the least impact to pneumatic systems already using the compressed air.
In an exemplary embodiment a system uses pressurized fluid to provide electrical power to a load. The system includes a pressurized fluid supply that provides fluid to a fluid motor, which provides power to a generator for generating electrical power supplied to a load and an energy storage device. A controller selects which of various sources within the system provides fluid to the fluid motor based on the operating mode of the system. When fluid supplied to the fluid motor is discontinued, the energy storage device discharges providing power to the load.
During operation, pressurized fluid runs a fluid motor that drives a high efficiency electrical generator to produce raw power. A control circuit adjusts the generator load such that as much power as possible is drawn from the generator given the pressure available. Energy in excess of that needed by the load is stored electrically in an energy storage device, such as an ultracapacitor. Once the energy storage device is fully charged, an electrically controlled valve shuts off the pressurized fluid supply to the fluid motor. When the pressurized fluid supply is turned off, the energy storage device supplies power to the load. Thus, a large amount of energy for a given fluid motor is extracted from the pressurized fluid supply, and the fluid motor does not continuously run which increases the overall elapsed lifetime of the fluid motor.